1. Field of the Invention
The invention relates to a control apparatus and control method for a transmission mounted in a vehicle. More particularly, the invention relates to a control apparatus and control method for a transmission that is connected to a driving power source via an automatic clutch.
2. Description of the Related Art
In a vehicle provided with a driving power source such as an engine (e.g., an internal combustion engine), an automatic transmission that automatically sets the optimum speed ratio between the engine and driving wheels is known as a transmission that appropriately transmits torque and rotation speed generated by the engine to the driving wheels according to the running state of the vehicle.
The automatic transmission mounted in the vehicle may be, for example, a planetary gear type transmission that sets the gear speed using clutches, brakes and a planetary gear set(s), or a belt type CVT (CVT: Continuously Variable Transmission) that adjusts the speed ratio smoothly (continuously) instead of in steps.
Also, another kind of transmission mounted in a vehicle is an automated manual transmission (AMT) that automatically performs a shift operation (i.e., changes the gear speed) using a shift actuator and a select actuator. An automatic clutch is used to connect this kind of automated manual transmission to a driving power source such as an engine.
The automatic clutch includes a friction type clutch and a clutch operating apparatus to operate the clutch. The clutch operating apparatus includes, for example, a hydraulic actuator for operating a release fork, and a hydraulic circuit for engaging and disengaging the clutch by controlling the hydraulic pressure of this actuator.
In the hydraulic circuit is provided an electromagnetic valve that is electrically operated, such as a solenoid valve that actuates a valve body by running current to an exciting coil. The release fork is operated by driving the actuator, which is done by controlling (i.e., selectively allowing or preventing) the flow of current to the exciting coil of the solenoid valve.
In the automatic clutch that is used with an automated manual transmission or the like, the clutch touch point (i.e., the point at which the clutch engages) changes depending on the friction and deformation and the like of the clutch so the clutch touch point must be learned in order to have the clutch always engage at the appropriate timing.
One example of clutch touch point learning (also referred to as “clutch neutral learning”) will be described. First, the clutch is automatically fully disengaged when a predetermined learning condition is satisfied, e.g., when the transmission is in neutral while the vehicle is stopped (idling). Next, at the point the output side of the clutch (i.e., the input side of the transmission) stops rotating, the clutch starts to be gradually automatically engaged. Then when the output side of the clutch reaches a predetermined rotation speed (such as 200 to 300 rpm), the clutch stroke (half clutch position) at this time is learned as the clutch touch point (see Japanese Patent Application Publication No. JP-A-2000-130476, for example).
Incidentally, with an automated manual transmission (AMT), it is desirable to update the learning value of the clutch touch point of the automatic clutch when the vehicle is stopped (i.e., idling) and the transmission is in neutral.
However, during or immediately after clutch touch point learning, the rotating body on the output side of the automatic clutch, i.e., the input rotating body that includes the input shaft and the input side gear set of the transmission, is rotating (at 200 to 300 rpm, for example). Therefore, if a gear shift is performed during or immediately after clutch touch point learning, a phenomenon will occur in which the rotation speed of the input rotating body is reduced by the transfer of energy between the input rotating body (in a rotating state) and the output rotating body (in a static state). As a result, inertia torque is generated when the rotation speed of that input rotating body is reduced, which may cause an unpleasant sensation for the driver.